Process for producing an electrolytic deposit of metallic chromium.



a ATES inzirn ENT 1 or nron. j

FRANZ sALZER, or vnnn'snnrr, GERMANY.

PROCESS FOR PRODUCING AN ELECTROLYTIC DEPOSIT 01E METALLIC GHROMIU'M.

j'ectof'the Emperor of Austria, residing in Dresden, Germany, at presentin Uj pest, near Budapest, Austria-Hungary, have invented certain newand- -useful..1mprovements in Processes for Producing an ElectrolyticDeposit of Metallic Chromium, of which the following is a specification.

It has been frequently tried to make a deposit ofmetallic chromium byelectrolysis on account of its great passivity and resistance againstchemical action and its hardness,

but all experiments made up to date have not succeeded in finding anymethod of practical use.

Various solutions of chromic salts and compounds have been used for thispurpose, which gave a cathodic deposit with great difficulty and veryhigh current density.-

By this invention it is possible to roduce easily a very coherent andfirm deposlt of any thickness, much harder than steel, very flexible andof fine color. I use for this purpose a bath composed of a mixture ofchromic acid and chromoxid in such proportions that the acid characteris greatly diminished, but enough chromic acid must be present to makethe bath conductive. Theoretically one could say that it consists mostlyof chromic 'chromate (lr.,O (Cr() with more or less oxid of chromiumthan is due to this formula, but it is better to have an excess of oxidthan the formula would demand.

According to the formula the proportion of weights of CrO and Cr O is 2:1, but the bath will'work better the more the weights of both compoundsget nearer and the proportion will be about constant during theelectrolysis. If for example a mixture is employed in which theproportion of (110 and Cr -O is 2 to 1, very much current will benecessary and the deposit .comparativel small. But if the proportion is4' to 3 or sti l nearer the bath works better. The quantity of chromiumcompounds contained in the solution may amount to 5. to 25 per cent. ofmetalhe chromium.

The bath can be prepared for instance by partial reduction of purechromicacid, by

means of an electric current or chemically or by a partial saturationof-CrO with Cr (0H,)

' or by partial'oxidation of chromium salts.

a-little acid will be advantageous.

Specification of Letters Patent.

is reduced by the cathode.

conditions of the beginning being maintained with a cathodic currentdensity of 2 to 5 amperes per sq. decimeter and 3 to 6 volts on anymetal, the surface of it being carefully,-

Patented Oct..'6, 1908, Application filed January 16, 1908.. Serial No.$11,138.

The bath works if duly prepared and the it is well known, need a greatamount of conductive salts in this bath only a very small amount of anelectrolyte is allowed, because a greater addition would produce at thecathode chromous oxid (CrO) or only hydrogen. There are different waysto keep the composition of the bath constant for instance by usinginsoluble anodes, which facilitate the oxidation of about as muchchromoxid to chromic acid,'as chromic acid Electrodes consisting offused ferro-ferric-oxid (Fe OQ, for instance, have this property. Ifother insoluble anodes are used as for instance lead or platinum, thecomposition of the bath can be maintained nearly unchanged if the anodesare partly separated from the cathodic solution by a diaphragm andpartly not separated. As the temperature will gradually rise while thecurrent passes, it is also very important to keep the temperatureconstant.- This may easily be done by'water cooling.

What I claim is 1. The process for producing an electrolytic deposit ofmetallic chromium by employing a bath containing chromic acid andchromoxid.

2. The process of producing an electrolytic deposit of metallic chromiumby employing a bath containing chromic acid and chromoxid, theproportionof chromoxid approximating that of the chromic acid.

3. The process for producing an electrolytic deposit of metallicchromium by employing a bath containing a mixture of a mixture ofchromic 'acid and chromoxid, chromic' acid being in excess.

4. The process for producing an electrolytic. deposit of metallicchromium by. em-

lo in a bath containing a mixture of chromic acid and chromoxid and asmall amount of an electrolyte. I

5 The process'for. producingan electrolytic deposit of metallic chromiumby em.

Ploy'ing' a-- bath containing -a mixture of chromic acid and chromoxidand. using anodes, which facilitate the oxidation of about the sameamount chromoxid to chromic acid,as chromic acid is reduced at thecathode by passing an electric current through the bath. I

6. The process for producing an electrolytic deposit of metallicchromium by emas chromic acid is reduced at theeathode by passing anelectric current through the bath.

7. The process for'producing an electrolytic deposit of metallicchromium by employing a bath containing a mixture of chromic acid andchromoxid and using anodes partly separated from the cathodic solutionby a diaphragm, and partly not separated.

*8. The process for producing an electrolytic deposit of metallicchromium by employing a bath containing a mixture of chromic acid andchromoxid and a small amount of an electrolyte and using anodes partlyseparated from the cathodic solution y a diaphragm, and partly notseparated.

9. The process for producing an electrolytic deposit of metallicchromium by employing a bath containing a mixture of chromic acidand'ehromoxid and by cooling the bath during'the passage of the current.

"10. Theprocess for roducing an electro FRANZ SALZER.

Witnesses SIGMUND BERNAUER, G. GUNDERMAN.

